1. Field of the Invention
The present invention relates to a method of sensing image information recorded on a film while the film is being fed past a sensor.
2. Description of the Related Art
An image data reading apparatus is known in which, while a film is being fed using a pulse motor, the film density is detected, an edge of a frame in which an image has been recorded is judged from a change in the film density, and image data is then read by a photosensor every time the film is fed through a predetermined distance (e.g., the reading or sensing width of the photosensor). In such apparatus, a judgement is made as to whether or not the film has been fed through a predetermined distance by using driving timing pulses which are applied to the pulse motor. This method involves, however, the following problem. Namely, due to the inertia acting on the rotor of the pulse motor and a rotary member secured to the rotor, the angle of rotation of the pulse motor which corresponds to one pulse in the timing pulse train for driving the pulse motor is not a constant value that is, the angle through which the motor rotates changes for successive drive pulses when the motor is accelerating or decelerating. As a result, it is not possible to read image data at evenly spaced positions along the film during periods of acceleration and deceleration.
For this reason, to sense the image information with a photosensor every time the film is fed through a predetermined length, it is conventional practice to employ a pulse generator for separately detecting the angle of rotation of the pulse motor and to determine the times at which image data is sensed on the basis of the detected rotational angle.
This conventional method still suffers, however, from the disadvantage that the employment of the pulse generator complicates the arrangement of the apparatus and leads to an increase in costs.